The present invention is particularly adapted for use with wastewater and stormwater systems, wherein components are buried beneath the earth. For example, wastewater may flow through plastic pipelines, i.e., circular conduits, running from a septic tank to a distribution box, and then to leaching chambers, galleries, etc.
The outer diameters of familiarly used pipes may vary from one installation to another, or within an installation, according to the installer's choice of the size and type of piping. For instance, the basic size may vary between 2, 3 and 4 inches. And for any nominal pipe size, the outer diameter may differ by a significant amount, according to the specification to which the piping conforms. For example, a 4 inch diameter SDR35 PVC (polyvinylchloride) pipe has an actual outside diameter of about 4.25 inches, while a 4 inch diameter Schedule 40 PVC pipe has an actual outside diameter of about 4.5 inches.
Leaching and stormwater system components, which are often connected by pipes, are typically made of molded plastic or concrete, uncommonly metal. It is an objective to have flexibility in installing such components, so that they can receive different size piping, and so there is a sufficient seal at the point of pipe entry, to prevent significant intrusion of soil and the like. It is also an objective to minimize the amount of labor in creating the seal and to keep component costs low.
To accomplish such objectives in the past, various embossed plastic seal assemblies have been commercially used. For concrete components, assemblies are separately formed and then molded into the wall of the component when it is cast. For plastic components, they are typically integrally formed when the article is molded. An aim of the seal might be to minimize extraneous water flow into or out of the component. More typically, the object is simply to prevent intrusion of surrounding soil into the component.
One general feature of many seal assemblies is to have a series of embossed or grooved circles, concentric or eccentric, where a pipe seal is desired. Thus, the installer can choose the one that fits the piping at hand. In the most basic embodiment, the installer uses a knife to cut along the embossing. In other seal designs, the embossing comprises a reduced thickness circle, or groove. The circular plastic piece contained within the groove is torn out by embossed pull tabs. For examples of such kind of prior art, see U.S. Pat. Nos. 4,805,920 and 5,882,014 to Gavin.
In other prior art seal assemblies, the pipe slips into a conical shaped seal, inboard of the exterior wall surface of the seal assembly. The seal expands radially, to make a tight conforming fit to the pipe. See U.S. Pat. No. 5,711,536 to Meyers. The prior art seals which are typically made of low density polyethylene (LDPE) have various advantages and disadvantages associated with their functionality, cost, ease of use, resistance to abuse, etc. LDPE has tear properties which make any tear out portion susceptible to comparatively easy tearing and removal, with various shapes and depths of grooves. And that kind of material provides the seal with a degree of compliance, so different pipe line entry angles can be accommodated.
When a pipe seal is molded as an integral part of an article, such as a molded leaching chamber or distribution box or other item, which has an interior concavity, there is more constraint on the complexity of seal assembly design, both because of mold considerations and because of the need to stack articles for shipment. Another design difficult, attending integrally molded seals relates to a contradiction in desired properties. When there is a pull-tab tear-out seal, rather inferior strength is desired at the point the tear is made. On the other hand, high tensile and tear strengths and good fracture toughness properties are desired for the whole of a typical component. Since the latter requirements tend to dominate, it becomes difficult to tear out some integrally molded seals, and their ease of use is lost. For example, the ASTM D1004 Graves Tear test shows that, compared to LDPE, initial tear resistance of polypropylene is 40–50 percent greater.
Another problem associated with tear out seals is that there is a tendency for a tear propagating in one groove to jump across the land to an adjacent closely spaced groove, thus producing a hole larger than wanted, and an ineffective seal results. Grooves associated with the two different outside diameters of commercial 4 inch pipe, mentioned above, are prone to this problem.